The present invention relates to wear resistant copper or copper base alloys, a method of preparing the wear resistant copper or copper base alloys and electrical parts using the wear resistant copper or copper base alloys. Particularly, the present hi invention relates to a copper base alloy having a surface which requires reduced friction or a reduced friction coefficient at the time of insertion/extraction like that of a multiple-pin connector used in electrical wiring or the like, for example, in an automotive vehicle, a surface which undergoes many times of insertion/extraction like that, for example, of a charging socket used in an electric automobile, a surface which requires wear resistance like that of a brush of a motor that is in contact with a rotor or a surface which requires wear resistance/corrosion resistance like that of a terminal of a battery, a method of preparation thereof and an electrical part using the copper base alloy.
By virtue of the recent electronic development, electrical wiring of various kinds of machines has become complicated and highly integrated and, along with this development, the connector has come to have multiple pins therein. A conventional Sn-plated connector has high frictional resistance at the time of insertion and extraction to give rise to a problem that it becomes difficult for the connector to be inserted.
Since an electric automobile of today requires to be recharged more than once a day, it is necessary for a socket component for use in charging to secure wear resistance. Moreover, an electric current with more than 10 A (amperes) flows through the components to generate heat; therefore, there has been a problem that a conventional method of Sn-plating or the like causes separation and so forth of a plating layer prepared by the method.
For the purpose of reducing insertion force of a Sn-plated terminal having multiple pins or of securing wear resistance or adhesion of an electrical part such as the above-described charging socket, there has been proposed until now a plan for enhancing an apparent hardness by first applying a hard nickel-plating or the like to a substrate under the Sn-plating or providing a Cuxe2x80x94Sn diffusion layer and then applying Sn plating on the thus applied hard nickel-plating or the thus provided Cuxe2x80x94Sn diffusion layer.
However, the above-described hard nickel plating has drawbacks of high price and poor workability. Moreover, the proposal that the Cuxe2x80x94Sn diffusion layer is provided and then the Sn plating is applied thereon necessitates extremely complicated steps such that Sn-plating is applied on the copper or copper base alloy, heat diffusion is conducted to produce a Cuxe2x80x94Sn layer and Sn plating is applied again on the thus produced Cuxe2x80x94Sn layer. This causes a cost problem, as well as poor adhesion and workability of the surface Sn-plating so that the proposal can not be practical.
Namely, it has become apparent that the conventional surface treatment technique can not solve the above-mentioned problems. Moreover, though a technique which performs heat diffusion between the base metal and the plating layer by the surface heat treatment has conventionally been available, the conventional technique is no more than preventing the separation of the surface treated layer from the substrate which can be caused by the working of the product or due to the thermal effect by causing the diffusion between the surface treated layer and the base metal. Thus, the conventional technique can not solve the above-described problems.
Therefore, it is an object of the present invention to solve the above-described problems and to provide copper or a copper base alloy which is excellent in surface hardness, contact resistance, bending workability, adhesion and terminal insertion force, particularly, to provide a connector material which corresponds to a recent higher packaging density of electrical parts such as electrical equipment for use in automobiles or the like and other electrical parts which require wear resistance and corrosion resistance.
The present invention has solved the above-mentioned problems and provides copper or a copper base alloy with a surface which has a small coefficient of friction and also an excellent electrical characteristic such as contact resistance, namely, it has a surface suitable, for example, for a connector or a charging socket for use in an electric automobile. The aimed product can be produced by appropriately forming a very hard Cuxe2x80x94Sn system intermetallic compound (a Cuxe2x80x94Sn intermetallic compound layer such as Cu3Sn, Cu4Sn, Cu6Sn5 or the like, or a compound layer having a composition such as a Cuxe2x80x94Snxe2x80x94X or the like wherein X is an additional element contained in the copper base alloy) and an oxide film layer with a controlled thickness on the surface of the copper or copper base alloy by first coating the surface thereof with Sn or a Sn alloy and then performing heat treatment. The present invention also provides a method of preparing the above proposed copper or copper base alloy as well as an electrical part utilizing the above proposed copper or copper base alloy.
The present invention is a technique which has been developed based on the following findings: by positively forming a Cuxe2x80x94Sn system intermetallic compound (Cu3Sn, Cu4Sn, Cu6Sn, or the like) which is excellent in surface hardness and contact resistance as well as an oxide film with a controlled thickness by defining a Sn film thickness to be applied to the base material and the conditions for heat treatment, it is possible to enhance the surface hardness of the surface layer to a level of Hv 250 or more, preferably Hv 300 or more; i.e., it is possible to improve the hardness of the surface layer to a level higher than the surface hardness of the Sn plating layer (Hv 60-120) or the hardness of the base material (Hv 80-250); it is possible to obtain an excellent slipping property by the presence of an oxide film with an appropriate thickness; and it is also possible to easily obtain contact resistance of 60 mxcexa9 or less. Thus, the present invention provides copper or a copper base alloy having an electrical characteristic, workability, the surface of a small coefficient of friction as well as excellent wear resistance suitable for use in a connector for an automobile or a charging socket or the like for an electric automobile. The invention also provides a method of preparing the above mentioned copper or copper base alloy as well as an electrical part utilizing the above mentioned copper or copper base alloy.
According to a first aspect of the present invention, there is provided a wear resistant copper or copper base alloy having formed on the outermost surface thereof an oxide film layer having a thickness of 10-1000 nm and also having a layer of an intermetallic compound primarily comprising Cuxe2x80x94Sn under the oxide film layer.
According to a second aspect of the present invention, there is provided a wear resistant copper or copper base alloy provided with an oxide film layer having a thickness of 10-1000 nm on an outermost surface thereof and an intermetallic compound primarily comprising Cuxe2x80x94Sn having a thickness of 0.1-10 xcexcm under the oxide film layer.
According to a third aspect of the present invention, there is provided a method of preparing a wear resistant copper or copper base alloy comprising the steps of:
coating copper or a copper base alloy with Sn; and
performing heat treatment to thereby form an oxide film layer having a thickness of 10-1000 nm on an outermost surface thereof and a layer of an intermetallic compound primarily comprising Cuxe2x80x94Sn under the oxide film layer.
According to a fourth aspect of the present invention, there is provided a method of preparing a wear resistant copper or copper base alloy comprising the steps of:
coating copper or a copper base alloy with Sn; and
performing heat treatment to thereby form an oxide film layer having a thickness of 10-1000 nm on an outermost surface thereof and a layer of an intermetallic compound having a thickness of 0.1-10, m primarily comprising Cuxe2x80x94Sn under the oxide film layer.
According to a fifth aspect of the present invention, there is provided a method of preparing a wear resistant copper or copper base alloy comprising the steps of:
coating copper or a copper base alloy with Sn;
performing reflow treatment; and
performing heat treatment to thereby form an oxide film layer having a thickness of 10-1000 nm on an outermost surface thereof and a layer of an intermetallic compound primarily comprising Cuxe2x80x94Sn under the oxide film layer.
According to a sixth aspect of the present invention, there is provided a method of preparing a wear resistant copper or copper base alloy comprising the steps of:
coating copper or a copper base alloy with Sn;
performing reflow treatment; and
performing heat treatment to thereby form an oxide film layer having a thickness of 10-1000 nm on an outermost surface thereof and a layer of an intermetallic compound primarily comprising Cuxe2x80x94Sn having a thickness of 0.1-10 xcexcm under the oxide film layer.
According to a seventh aspect of the present invention, there is provided an electrical part comprising a wear resistant copper or copper base alloy with an oxide film layer having a thickness of 10-1000 nm formed on an outermost surface thereof and a layer of an intermetallic compound primarily comprising Cuxe2x80x94Sn formed under the oxide film layer.
According to an eighth aspect of the present invention, there is provided an electrical part comprising a wear resistant copper or copper base alloy with an oxide film layer having a thickness of 10-1000 nm formed on an outermost surface thereof and a layer of an intermetallic compound primarily comprising Cuxe2x80x94Sn having a thickness of 0.1-10 xcexcm formed under the oxide film layer.
According to a ninth aspect of the present invention, there is provided an electrical part comprising a wear resistant copper or copper base alloy prepared by a method comprising the steps of:
coating copper or a copper base alloy with Sn; and
performing heat treatment to thereby form an oxide film layer having a thickness of 10-1000 nm on an outermost surface thereof and a layer of an intermetallic compound primarily comprising Cuxe2x80x94Sn under the oxide film layer.
According to a tenth aspect of the present invention, there is provided an electrical part comprising a wear resistant copper or copper base alloy prepared by a method comprising the steps of:
coating copper or a copper base alloy with Sn; and
performing heat treatment to thereby form an oxide film layer having a thickness of 10-1000 nm on an outermost surface thereof and a layer of an intermetallic compound primarily comprising Cuxe2x80x94Sn having a thickness of 0.1-10 xcexcm under the oxide film layer.
According to an eleventh aspect of the present invention, there is provided an electrical part comprising a wear resistant copper or copper base alloy prepared by a method comprising the steps of:
coating copper or a copper base alloy with Sn;
performing reflow treatment; and
performing heat treatment to thereby form an oxide film layer having a thickness of 10-1000 nm on an outermost surface thereof and a layer of an intermetallic compound primarily comprising Cuxe2x80x94Sn under the oxide film layer.
According to a twelfth aspect of the present invention, there is provided an electrical part comprising a wear resistant copper or copper base alloy produced by a method comprising the steps of:
coating copper or a copper base alloy with Sn;
performing reflow treatment; and
performing heat treatment to thereby form an oxide film layer having a thickness of 10-1000 nm on an outermost surface thereof and a layer of an intermetallic compound primarily comprising Cuxe2x80x94Sn having a thickness of 0.1-10 xcexcm under the oxide film layer.
According to a thirteenth aspect of the present invention, there is provided the wear resistant copper or copper base alloy described in the first or second aspect in which contact resistance thereof is 60 mxcexa9 or less.
According to a fourteenth aspect of the present invention, there is provided the method of preparing the wear resistant copper or copper base alloy described in the third to sixth aspects in which contact resistance thereof is 60 mxcexa9 or less.
According to a fifteenth aspect of the present invention, there is provided the electrical part described in the seventh to twelfth aspects in which contact resistance of the copper or copper base alloy is 60 mxcexa9 or less.
According to a sixteenth aspect of the present invention, there is provided the copper or copper base alloy described in the first, second or thirteenth aspect in which surface hardness thereof is Hv 250 or more.
According to a seventeenth aspect of the present invention, there is provided the method of preparing the wear resistant copper or copper base alloy described in the third to sixth aspects or the fourteenth aspect in which surface hardness thereof is Hv 250 or more.
According to an eighteenth aspect of the present invention, there is provided the electrical part described in the seventh to twelfth aspects or the fifteenth aspect, in which surface hardness thereof is Hv 250 or more.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.